Aqueous Dispersions of Polymers which Comprise a Fluorescent Dye, Process for Their Production and Their Use for Marking Materials

ABSTRACT

Aqueous dispersions of polymers which are obtainable by free radical suspension polymerization of ethylenically unsaturated monomers in an oil-in-water emulsion whose disperse phase comprises at least one fluorescent dye dissolved in at least one ethylenically unsaturated monomer and has an average particle diameter of at least 1 μm, in the presence of at least one surface-active compound and at least 0.5% per weight, based on the monomers, of at least one hydrophobic, nonpolymerizable organic compound, of a hydrophobic polymer of at least one C 2 - to C 6 -olefin having a molar mass M w  of up to 10 000, of a siloxane having a molar mass M w  of up to 5000 and/or polystyrene having a molar mass M w  of up to 10 000, processes for the preparation of these dispersions and use of aqueous dispersions of polymers which are obtainable by free radical suspension polymerization or by free radical miniemulsion polymerization of ethylenically unsaturated monomers in an oil-in-water emulsion whose disperse phase comprises at least one fluorescent dye in at least one ethylenically unsaturated monomer and has an average particle diameter of at least 100 nm, in the presence of at least one surface-active compound and at least 0.5% by weight, based on the monomers, of at least one hydrophobic, nonpolymerizable, organic compound, of a hydrophobic polymer of at least one C 2 - to C 6 -olefin having a molar mass M w  of up to 10 000, of a siloxane having a molar mass M w  of up to 5000 and/or polystyrene having a molar mass M w  of up to 10 000 and of the powders obtainable from these polymer dispersions in each case by drying and comprising at least one fluorescent dye for the marking of materials.

The invention relates to aqueous dispersions of polymers which have aparticle diameter of at least 1 μm and comprise a fluorescent dye,processes for the preparation of such dispersions by free radicalsuspension polymerization of ethylenically unsaturated monomers in anoil-in-water emulsion whose disperse phase comprises at least onefluorescent dye dissolved in at least one ethylenically unsaturatedmonomer and has an average particle diameter of at least 1 μm, in thepresence of at least one surface-active compound, and the use of theaqueous dispersions thus obtainable or of the polymer powders obtainabletherefrom for the marking of materials.

WO-A-99/40123 discloses a process for the preparation of aqueous polymerdispersions whose dispersed polymer particles comprise an organic dyedistributed homogeneously, i.e. as a molecular dispersion. Such aqueousdispersions are prepared by miniemulsion polymerization by polymerizingethylenically unsaturated monomers which comprise a dissolved organicdye, in the form of an oil-in-water emulsion in the presence ofpolymerization initiators forming free radicals, the disperse phase ofthe emulsion being formed substantially by dye-containing monomerdroplets having a diameter of <500 nm. In an advantageous embodiment ofthe invention, monomer mixtures which comprise crosslinking monomers areused in the polymerization. The polymer dispersions are stable tosedimentation. The dispersed particles have an average particle diameterof from 100 to 400 nm. They can be obtained from the aqueous dispersionswith the aid of conventional drying methods. The dye-containing polymerdispersions are used, for example, for the pigmenting of high molecularweight organic and inorganic materials, and for the pigmenting ofprinting inks and of inks for inkjet printing.

Further dye-containing polymer dispersions whose dye-containing polymerparticles have an average particle diameter below 1000 nm are disclosedin EP-A-1 191 041. Suitable colorants in addition to organic dyes arealso UV absorbers and optical brighteners. They are prepared bydissolving a colorant in at least one ethylenically unsaturated monomer,emulsifying this solution in water with formation of a conventionalmacroemulsion, homogenizing the macroemulsion with formation of aminiemulsion having an average droplet size below 1000 nm andpolymerizing the miniemulsion in the presence of a free radicalpolymerization initiator, from 0.1 to 20% by weight of at least onenonionic surface-active compound and from 1 to 50% by weight, based ineach case on the monomers used, of at least one amphiphilic polymer. Thepolymer particles comprise from 0.5 to 50% by weight of at least onehomogeneously distributed organic dye, optical brightener or UVabsorber, which is to be understood as meaning that the organiccolorants are dissolved in monomolecular form in the polymer matrix orare present in the form of bimolecular or higher molecular aggregates.

WO-A-2004/037867 discloses aqueous polymer dispersions which comprisealkyldiketenes and are obtainable by miniemulsion polymerization ofhydrophobic monoethylenically unsaturated monomers in the presence ofalkyldiketenes. These dispersions are used as sizes for paper and aswater repellents for leather, natural and/or synthetic fibers andtextiles.

B. J. Battersby, G. A. Lawrie, A. P. R. Johnston and M. Trau, in Chem.Commun., 2002, 1435-1441, report on optical coding of colloidalsuspensions with fluorescent dyes, nanocrystals and metals. Thus, forexample, colloids having a diameter of from 3 to 6 μm were opticallymarked by incorporating fluorescent dyes or complexed lanthanides.Another method for marking colloids consists in the incorporation ofzinc sulfide which is provided with cadmium selenide nanocrystals or inthe electrochemical deposition of metal ions in cavities of colloids.The colloids can be distinguished from one another, for example, withthe aid of a fluorescence microscope or of a cytometer.

WO-A-99/52708 discloses a process for the marking of gaseous, liquid orsolid materials, a sufficient amount of colored microparticles and/ornanoparticles which are bound to carrier microparticles being added to agaseous, liquid or solid material which is to be subsequentlyidentified. The particles used consist, for example, of crosslinkedpolystyrene and have a diameter of about 5.5 μm. The particles arestained or coded, for example, with three different fluorescent dyes ineight different concentrations of the dyes so that 512 different groupsof coded particles are obtained. The individual groups can beidentified, for example, with the aid of a cytometer. The codedparticles are used for the marking of substances, e.g. sodium chloridecrystals, in order, for example, to verify the manufacturer, theproduction batch and the production date in this way.

DE-A 2004 027 416 discloses a process for the marking of materials withcoded microparticies, the coded microparticles used being obtainable by

-   (i) polymerization of at least one water-soluble monoethylenically    unsaturated monomer in the presence of at least one ethylenically    unsaturated monomer having at least two double bonds in the molecule    by inverse water-in-oil suspension polymerization in the presence of    doped nanoparticles as a suspending medium,-   (ii) emulsion polymerization of water-insoluble monoethylenically    unsaturated monomers with from 0 to 10% by weight, based on the    monomer mixture, of at least one ethylenically unsaturated monomer    having at least two double bonds in the molecule, doped    nanoparticles being used as an emulsifier for stabilizing the    disperse phase,-   (iii) polymerization of at least one ethylenically unsaturated    monomer together with a copolymerizable dye which has an    ethylenically unsaturated double bond and, if appropriate,    agglomeration of these particles,-   (iv) adsorption of at least one dye onto a virtually water-insoluble    polymer particle, and, if appropriate, agglomeration of these    particles,-   (v) agglomeration of at least two different groups of microparticles    which differ in their absorption, emission and/or scattering of    electromagnetic radiation to give agglomerates having an average    particle diameter of from 300 nm to 500 μm,-   (vi) precipitation of at least one water-insoluble dye from a    solution in at least one water-miscible organic solvent onto a    virtually water-insoluble polymer particle or-   (vii) precipitation by electrostatic attraction of water-soluble    dyes onto oppositely charged virtually water-insoluble polymer    particles.

For example, nanoparticles which are doped with at least one dye or acompound from the group consisting of the rare earth metals of thePeriodic Table of the Elements or which are radioactive are used in thepolymerization according to (i) and (ii).

EP-B-0 692 517 discloses a process for the preparation of fluorescentpigments, a mixture of

-   (A) from 69.9 to 99.8% by weight of a C₁-C₈-alkyl ester of acrylic    or methacrylic acid,-   (B) from 0 to 29.9% by weight of a copolymerizable,    monoethylenically unsaturated monomer,-   (C) from 0.1 to 30.0% by weight of a copolymerizable,    polyfunctional, crosslinking monomer being polymerized in the    presence of-   (D) from 0.1 to 15.0% by weight, based on the sum of (A) and (B), of    a nonpolar fluorescent dye from the coumarin and perylene series.    being polymerized in suspension. The diameter of the polymer    particles dispersed in water and comprising a fluorescent dye is in    the range of from 0.1 to 3 mm if the monomers are emulsified in    water with the aid of an impeller stirrer and from 1 to 100 μm if    the monomers are emulsified in water with the aid of units having a    strong shearing effect, such as Ultra-Turrax®, and the emulsions are    then polymerized. However, the aqueous polymer dispersions thus    obtainable have a broad particle size distribution.

It is the object of the invention to provide aqueous dispersions ofpolymers which have a particle diameter of at least 1 μm and whichcomprise a fluorescent dye, having as uniform a particle sizedistribution as possible. Such polymer dispersions are of interest inparticular for single-particle analysis because particle sizes of, forexample, from 1 to 100 μm can be particularly advantageously determinedanalytically.

The object is achieved, according to the invention, by aqueousdispersions of polymers which have a particle diameter of at least 1 μmand which comprise a fluorescent dye, which are obtainable by freeradical suspension polymerization of ethylenically unsaturated monomersin an oil-in-water emulsion whose disperse phase comprises at least onefluorescent dye dissolved in at least one ethylenically unsaturatedmonomer and has an average particle diameter of at least 1 μm, in thepresence of at least one surface-active compound and at least 0.5% byweight, based on the monomers, of at least one hydrophobic,nonpolymerizable, organic compound, of hydrophobic polymers of at leastone C₂- to C₆-olefin having a molar mass M_(w) of up to 10 000, of asiloxane having a molar mass M_(w) of up to 5000 and/or polystyrenehaving a molar mass M_(w) of up to 10 000.

The synthesis of the polymer particles dispersed in water is effected,according to the invention, by suspension polymerization. In contrast tothe process which is disclosed in the abovementioned EP-B-0692 517 acosolvent which is only very slightly soluble in water and is intendedfor the fluorescent dye is used as a hydrophobic substance in theprocess according to the invention, in addition to the monomers, atleast one fluorescent dye and a surface-active compound. The watersolubility of the hydrophobic substance is, for example, <0.1 g/l,preferably <0.01 g/l (at 25° C. and at 1013 mbar). It is possible to useall hydrophobic compounds which are usually used in miniemulsionpolymerization, cf. WO-A-99/40123, page 7, line 27 to page 8, line 20.In contrast to the preparation of a miniemulsion, however, according tothe invention shearing is not effected to such a great extent in theemulsification of the solution comprising at least one fluorescent dyeand comprising at least monomers and a hydrophobic substance in water,so that an oil-in-water emulsion having an average particle size of atleast 1 μm is obtained. The average particle size of the oil-in-wateremulsion is therefore substantially above the particle size customary inthe case of miniemulsions. The dispersed polymer particles whichcomprise the uniformly distributed fluorescent dye form from theemulsified monomer droplets. This process can also be referred to asminisuspension polymerization.

According to the invention, aqueous dispersions of polymers whichcomprise at least one fluorescent dye, have an average particle size inthe range of from 1 to 100 μm and have a narrower particle sizedistribution than the polymer dispersions which are prepared withexclusion of hydrophobic compounds (cf. EP-B-0 692 517) are obtained.Compared with the known process, less coagulum is formed in the processaccording to the invention and in addition the emulsion polymerizationas a secondary reaction is very substantially suppressed.

Suitable ethylenically unsaturated monomers are, for example,

-   (a) hydrophobic monomers from the group consisting of C₁- to    C₁₈-alkyl esters of acrylic acid, C₁- to C₁₈-alkyl esters of    methacrylic acid, vinyl acetate, vinyl propionate, vinyl butyrate,    styrene, chlorostyrene and/or α-methylstyrene,-   (b) if appropriate, hydrophilic monomers from the group consisting    of ethylenically unsaturated C₃- to C₆-carboxylic acids,    vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,    sulfopropyl acrylate, sulfopropyl methacrylate, styrenesulfonic    acid, salts of said acids, acrylonitrile, methacrylonitrile, C₁- to    C₈-hydroxyalkyl esters of C₁- to C₆-carboxylic acids, di-C₁- to    C₃-alkylamino-C₂- to C₄-alkyl acrylate, di-C₁- to C₃-alkylamino-C₂-    to C₄-alkyl methacrylates, acrylamide, methacrylamide,    N-vinylformamide and/or N-vinylpyrrolidone and-   (c) if appropriate, at least one crosslinking monomer having at    least two double bonds in the molecule.

The monomers of group (a) can be used alone, as a mixture of one anotherand in combination with the monomers (b) and/or (c) in the suspensionpolymerization. Examples of monomers of group (a) are methyl acrylate,ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate,isobutyl acrylate, tert-butyl acrylate, secbutyl acrylate, pentylacrylate, n-hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, decylacrylate, dodecyl acrylate, palmityl acrylate, stearyl acrylate, methylmethacrylate, ethyl methacrylate, isopropyl methacrylate, n-propylmethacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butylmethacrylate, tert-butyl methacrylate, pentyl methacrylate, n-hexylmethacrylate, cyclohexyl methacrylate, heptyl methacrylate, 2-ethylhexylmethacrylate, octyl methacrylate, decyl methacrylate, dodecylmethacrylate, palmityl methacrylate and stearyl methacrylate and vinylacetate, vinyl propionate, vinyl butyrate, styrene, chlorostyrene and/orα-methylstyrene. Preferably used monomers of this group are methylmethacrylate and styrene.

Monomers of group (b), which, if appropriate, are used for thehydrophilic modification of the polymers, are selected, for example,from the group consisting of the ethylenically unsaturated C₃- toC₆-carboxylic acids, vinylsulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, sulfopropyl acrylate,sulfopropyl methacrylate, styrenesulfonic acid, salts of said acids,acrylonitrile, methacrylonitrile, C₁- to C₈-hydroxyalkyl esters of C₁-to C₆-carboxylic acids, di-C₁- to C₃-alkylamino-C₂- to C₄-alkylacrylates, di-C₁- to C₃-alkylamino-C₂- to C₄-alkyl methacrylates,acrylamide, methacrylamide, N-vinylformamide and/or N-vinylpyrrolidone.

Examples of ethylenically unsaturated carboxylic acids are acrylic acid,methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconicacid and vinylacetic acid. The ethylenically unsaturated carboxylicacids and the monomers comprising sulfo groups can be used in thepolymerization in the form of the free acids and in a form partly orcompletely neutralized with alkaline metal bases, alkaline earth metalbases, ammonia or amines. In general, the sodium, potassium or ammoniumsalts of the acidic monomers are used. The acidic monomers can, however,also be neutralized with amines, such as butylamine, morpholine,ethanolamine, diethanolamine or triethanolamine, and used in partly orcompletely neutralized form in the polymerization. Among thehydroxyalkyl esters, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate and2-hydroxypropyl methacrylate are particularly suitable.

Examples of basic monomers are dimethylaminoethyl acrylate,dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate,dimethylaminopropyl methacrylate, diethylaminoethyl acrylate,diethylaminoethyl methacrylate, di-n-propylaminoethyl acrylate anddi-n-propylaminoethyl methacrylate. The basic monomers can be used inthe polymerization as a free base, as a salt with mineral acids,saturated carboxylic acids or sulfonic acids, such as p-toluenesulfonicacid or benzenesulfonic acid, and in quaternized form, (e.g. quaternizedwith methyl chloride, ethyl chloride, n-propyl chloride, dimethylsulfate, n-hexyl chloride, cyclohexyl chloride or benzyl chloride).

The monomers of group (b) can be used individually or in combination inthe polymerization. Preferably, acrylic acid, methacrylic acid,acrylamide, methacrylamide, vinylformamide and N-vinylpyrrolidone areused from this group.

Crosslinking monomers having at least two double bonds in the moleculeare used as monomers of group (c). Examples of such monomers are estersof polyhydric alcohols and ethylenically unsaturated carboxylic acids,such as acrylic acid or methacrylic acid, e.g. ethylene glycoldiacrylate, ethylene glycol dimethacrylate, butanediol diacrylate,butanediol dimethacrylate, hexanediol diacrylate, hexanedioldimethacrylate, acrylates and methacrylates of polyalkylene glycols,such as polyethylene glycols, polypropylene glycols or block copolymersof ethylene oxide and propylene oxide having molar masses of, forexample, from 100 to 5000, allyl acrylate, allyl methacrylate,trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,pentaerythrityl triacrylate, pentaerythrityl trimethacrylate,pentaerythrityl tetraacrylate, pentaerythrityl tetramethacrylate,divinylbenzene, divinylurea and methylenebisacrylamide. Allylmethacrylate, butanediol 1,4-diacrylate and trimethylolpropanetriacrylate are preferred as crosslinking agents.

The monomer mixtures used in the polymerization comprise, for example,

-   (a) from 60 to 100% by weight of at least one hydrophobic monomer,-   (b) from 0 to 30% by weight of at least one hydrophilic monomer and-   (c) from 0 to 40% by weight of at least one crosslinking monomer    having at least two double bonds.

Monomer mixtures which comprise

-   (a) from 60 to 99.9% by weight of at least one hydrophobic monomer,-   (b) from 0 to 30% by weight of at least one hydrophilic monomer and-   (c) from 0.1 to 25% by weight, in particular from 5 to 15% by    weight, of at least one crosslinking monomer    are preferably used in the polymerization.

Fluorescent dyes are known to the person skilled in the art. They aredescribed, for example, in WO-A-99/40123, page 10, line 14 to page 25,line 25, mentioned in connection with the prior art, and in EP-B-0 692517, page 3, line 7 to page 6, line 1. Suitable fluorescent dyes belong,for example, to the class consisting of the coumarin, perylene,terrylene, quaterrylene, naphthalimide, cyanine, xanthene, oxazine,anthracene, naphthacene, anthraquinone or thiazine dyes. Thosefluorescent dyes which have a higher solubility in the oil phase than inthe aqueous phase of the oil-in-water emulsion are preferably used. Forexample, the dyes should have a solubility of at least 0.001% by weight,preferably of at least 0.01% by weight, in the oil phase.

In order to prepare aqueous dispersions of finely divided polymers whichcomprise a fluorescent dye and have an average particle diameter of atleast 1 μm, it is possible, for example, to adopt a procedure in whichfirst at least one fluorescent dye is dissolved in a mixture of at leastone of the suitable monomers and at least one hydrophobic compound andthis solution is then emulsified in an aqueous phase which comprises atleast one surface-active compound. The emulsification of the oil phasein the aqueous phase can be carried out, for example, with the aid of ahigh-speed stirrer or with the aid of apparatuses which operateaccording to the rotor-stator principle, such as Ultra-Turrax®).Oil-in-water emulsions having an average particle size of the oildroplets of from at least 1 μm to 100 μm, preferably from 1.1 to 25 μm,are obtained.

A substantial constituent of the aqueous dispersions, according to theinvention, of polymers which comprise at least one fluorescent dye is ahydrophobic substance. Examples of this are hydrophobic,nonpolymerizable, organic compounds, hydrophobic polymers of at leastone C₂- to C₆-olefin having a molar mass M_(w) of up to 10 000,siloxanes having a molar mass M_(w) of up to 5000 and/or polystyreneshaving a molar mass M_(w) of up to 10 000. Hydrophobic,nonpolymerizable, organic compounds are to be understood as meaning allcompounds which have, for example, a solubility in water of <0.01 g/l(at 25° C. and 1013 mbar). Examples of these are aliphatic or aromatichydrocarbons having 10 to 50 carbon atoms, preferably having 10 to 24carbon atoms, alcohols having 10 to 24 carbon atoms, tetraalkylsilanes,olive oil, perfluoromethyidecaline and/or di-n-butyl esters of C₄- toC₆-dicarboxylic acids.

Particularly preferably used hydrophobic compounds from this group arehexadecane and liquid paraffins, such as industrial or medical whiteoil. Such a white oil is available, for example, under CAS No.8042-47-5. This is a petroleum mineral oil as a complex combination ofsaturated hydrocarbons having carbon numbers in the range from C15 toC50. It is also possible to use mixtures of hydrophobic,nonpolymerizable organic compounds, for example mixtures of hexadecaneand white oil. Like the other hydrophobic compounds, it is used, forexample, in an amount of from 0.5 to 50% by weight, preferably in anamount of from 1 to 20% by weight, based on the monomers.

Further suitable hydrophobic substances are homopolymers of at least oneC₂- to C₆- olefin or copolymers of C₂- to C₆-olefins having a molar massM_(w) of up to 10 000. Polymers of this type are, for example,

-   (i) homopolymers of ethylene, propylene, 1-butene, 2-butene,    1-pentene or 1-hexene, having an average molar mass M_(w) of from    100 to 1000,-   (ii) copolymers of at least two of the monomers mentioned under (i)    and having an average molar mass M_(w) of from 100 to 1000 and/or-   (iii) polyisobutylene having an average molar mass M_(w) of at least    100.

Examples of polymers of group (i) are low molecular weight homopolymersof ethylene, propylene, 1-butene, 1-pentene, and 1-hexene. These are,for example, oligomers of ethylene, such as, in particular, polymerscomprising 8 or 12 carbon atoms per molecule, which are offered by Shellunder the brand Neodene® and by BP as alpha-olefin, e.g. AO 2026 and byChevron-Philips Corporation. The tetramer propene available fromExxon-Mobil and the tetrabutene sold by Oxeno are also suitable ascompound (i). The compounds (i) comprise a double bond. They have, forexample, an average molar mass M_(w) of from 100 to 10 000, preferablyfrom 150 to 2000.

Examples of compounds (ii) are copolymers of ethylene and propylene,copolymers of ethylene and 1-butene, copolymers of ethylene and2-butene, copolymers of ethylene and 1-hexene, copolymers of propyleneand 1-butene and copolymers of propylene, 1-butene and 2-butene andfurther combinations. These copolymers also comprise an ethylenicallyunsaturated double bond. They have, for example, average molar massesM_(w) of from 100 to 10 000, preferably from 150 to 2000.

Polyisobutylenes are suitable as compounds of group (iii). They have,for example, an average molar mass M_(w) of at least 100, preferably atleast 150. The average molar masses M_(w) are, for example, in the rangeof from 200 to 10 000. In general, the average molar mass M_(w) of thesuitable polyisobutylenes is at least 400 and preferably in the range offrom 500 to 4000.

Suitable polyisobutylenes are commercially available. Examples of theseare the Glissopal® brands and Oppanol® brands from BASFAktiengesellschaft, such as Glissopal® 550, Glissopal® 1000, Glissopal®1300, Glissopal® 2300, Oppanol B10 and B12. Polyisobutylene is prepared,for example, by cationic polymerization of isobutene under BF₃catalysis. These polyisobutylenes have a high content of α-olefingroups, which is, for example, at least 80%, preferably at least 85%.They can also be prepared by so-called “living” polymerization usingLewis acids other than BF₃, such as AIY₃, TiY₄, SnY₄ and ZnY₂, thesubstituent Y in the preceding formulae being fluorine, chlorine,bromine or iodine. Polyisobutylenes having a content of at least 80% ofα-olefin groups are preferably used. Further examples of compounds to beused according to the invention as (iii) are the polyisobutylenesoffered by BP under the name Indopol® and having the designationsL2-L-50 and H-7 to H-18 000 which have a molar mass in the range of from180 to 6000. These polyisobutylenes likewise comprise α-olefin groups,but only up to about 10%.

Depending on the polymerization process, the polydispersity index (PDI)for these polymers, i.e. the ratio of weight average and number averagemolecular weight, is in the range of from 1.05 to 10, preferably in therange of from 1.05 to 5 and in particular in the range of from 1.05 to2.0. The method of determination of the polydispersity (PDI) and of thenumber average and weight average molecular weight is described, forexample, in Analytiker-Taschenbuch, volume 4, pages 433 to 442, Berlin1984.

Preferably used hydrophobic compounds from these groups are, forexample, (i) tetramer propene and tetrameric butene, (ii) copolymers ofethylene and propylene, copolymers of ethylene and 1-butene, copolymersof ethylene and 2-butene, copolymers of ethylene and 1-hexene,copolymers of propylene and 1-butene and copolymers of propylene,1-butene and 2-butene having a molar mass of in each case from 150 to2000 and/or (iii) polyisobutylenes having a molar mass in the range offrom 200 to 10 000.

Further suitable hydrophobic substances are siloxanes having a molarmass M_(w) of up to 5000 and/or polystyrenes having a molar mass M_(w)of up to 10 000.

In order to stabilize the oil-in-water emulsion, at least onesurface-active compound is usually used. The surfactant is used, forexample, in amounts of up to 15% by weight, for example from 0.05 to 15%by weight, preferably from 0.05 to 5% by weight and in particular from0.1 to 2% by weight, based in each case on the total dispersion. It ispresent either in the aqueous phase, in the organic phase or in bothphases. It is preferably added to the aqueous phase before theemulsification. In principle, all surfactants may be used. Preferablyused surfactants are anionic and/or nonionic surfactants and amphiphilicpolymers having average molar masses M_(w) of, for example, from 1000 to100 000. Examples of suitable surfactants are sodium lauryl sulfate,sodium dodecyl sulfate, sodium hexadecyl sulfate, sodium dioctylsulfosuccinate and/or adducts of from 15 to 50 mol of ethylene oxideand/or propylene oxide and 1 mol of a C₁₂- to C₂₂-alcohol.

The oil-in-water emulsion may additionally be stabilized with the aid ofamphiphilic polymers, which, if appropriate, are used. If amphiphilicpolymers are used they are employed in amounts of, for example, from0.05 to 15% by weight, preferably from 0.5 to 5% by weight, based on themonomers used in the polymerization. Examples of amphiphilic polymersare copolymers which comprise units of

-   (i) hydrophobic monoethylenically unsaturated monomers and-   (ii) monoethylenically unsaturated carboxylic acids,    monoethylenically unsaturated sulfonic acids, monoethylenically    unsaturated phosphonic acids or mixtures thereof and/or basic    monomers.

Suitable hydrophobic monoethylenically unsaturated monomers

-   (i) are, for example, styrene, methylstyrene, ethylstyrene,    acrylonitrile, methacrylonitrile, C₂- to C₁₈-olefins, esters of    monoethylenically unsaturated C₃- to C₅-carboxylic acids, and    polyhydric alcohols, vinyl alkyl ethers, vinyl esters or mixtures    thereof. From this group of monomers, isobutene, diisobutene,    styrene and acrylates such as ethyl acrylate, isopropyl acrylate,    n-butyl acrylate and sec-butyl acrylate are preferably used.

The amphiphilic copolymers comprise, as hydrophilic monomers

-   (ii) preferably acrylic acid, methacrylic acid, maleic acid, maleic    anhydride, itaconic acid, vinylsulfonic acid,    2-acrylamidomethylpropanesulfonic acid, acrylamidopropane-3-sulfonic    acid, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate,    styrenesulfonic acid, vinylphosphonic acid or mixtures thereof    incorporated in the form of polymerized units. The acidic monomers    can be present in the form of the free acids or in partly or    completely neutralized form.

Further suitable hydrophilic monomers are basic monomers. They can bepolymerized with the hydrophobic monomers (i) alone or as a mixture withthe abovementioned acidic monomers. If mixtures of basic acidic monomersare used, amphoteric copolymers which, depending on the molar ratio ofacidic to basic monomers incorporated in each case in the form ofpolymerized units, are anionically or cationically charged.

Basic monomers are, for example, di-C₁- to C₂-alkylamino-C₂- to C₄-alkyl(meth)acrylates or diallyldimethylammonium chloride. The basic monomerscan be present in the form of the free bases, of the salts with organicor inorganic acids or in the form quaternized with alkyl halides. Thesalt formation or the quaternization, in which the basic monomers becomecationic, can be effected partially or completely. Examples of suchcompounds are dimethylaminoethyl methacrylate, diethylaminoethylmethacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate,dimethylaminopropyl methacrylate, dimethylaminopropyl acrylate,diethylaminopropyl methacrylate, diethylaminopropyl acrylate and/ordimethylaminoethyl acrylamide, dimethylaminoethyl methacrylamide,dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamideand/or diallyldimethylammonium chloride.

If the amphiphilic copolymers are not sufficiently water-soluble in theform of the free acid they are used in the form of water-soluble salts;for example the corresponding alkali metal, alkaline earth metal andammonium salts are used. These salts are prepared, for example, bypartial or complete neutralization of the free acid groups of theamphiphilic copolymers with bases; for example, sodium hydroxidesolution, potassium hydroxide solution, magnesium oxide, ammonia oramines such as triethanolamine, ethanolamine, morpholine, triethylamineor butylamine, are used for the neutralization. The acid groups of theamphiphilic copolymers are preferably neutralized with ammonia or sodiumhydroxide solution. The water solubility of basic monomers or ofcopolymers which comprise such monomers incorporated in the form ofpolymerized units can on the other hand be increased by partial orcomplete neutralization with a mineral acid, such as hydrochloric acidor sulfuric acid, or by addition of an organic acid, such as acetic acidor p-toluenesulfonic acid. The molar mass of the amphiphilic copolymersis, for example, from 1000 to 100 000 and is preferably in the range offrom 1500 to 10 000. The acid numbers of the amphiphilic copolymers are,for example, from 50 to 500, preferably from 150 to 350 mg KOH/g ofpolymer.

Particularly preferred amphiphilic copolymers are those which comprise

-   (i) from 95 to 45% by weight of isobutene, diisobutene, styrene or    mixtures thereof and-   (ii) from 5 to 55% by weight of acrylic acid, methacrylic acid,    maleic acid, monoesters of maleic acid or mixtures thereof    incorporated in the form of polymerized units. Copolymers which    comprise-   (i) from 45 to 80% by weight of styrene,-   (ii) from 55 to 20% by weight of acrylic acid and, if appropriate,-   (iii) additionally further monomers incorporated in the form of    polymerized units are preferably used as a stabilizer for the    miniemulsion. The copolymers can, if appropriate, comprise units of    monoesters of maleic acid incorporated in the form of polymerized    units as further monomers (iii). Such copolymers are obtainable, for    example, by copolymerizing copolymers from styrene, diisobutene or    isobutene or mixtures thereof with maleic anhydride in the absence    of water and treating the copolymers with alcohols after the    polymerization, from 5 to 50 mol % of a monohydric alcohol being    used per mole of anhydride groups in the copolymer. Suitable    alcohols are, for example, methanol, ethanol, n-propanol,    isopropanol, n-butanol, isobutanol and tert-butanol. However, it is    also possible to react the anhydride groups of the copolymers with    polyhydric alcohols, such as glycol or glycerol. Here, however, the    reaction is continued only until only one OH group of polyhydric    alcohol reacts with the anhydride group. If the anhydride groups of    the copolymers are not completely reacted with alcohols,    ring-opening of the anhydride groups not reacted with alcohols takes    place as a result of addition of water.

Other compounds suitable as a stabilizer for oil-in-water emulsions are,for example, commercially available polymers of monoethylenicallyunsaturated acids and graft polymers of N-vinylformamide on polyalkyleneglycols, which are described, for example, in WO-A-96/34903. Thegrafted-on vinylformamide units can, if appropriate, be hydrolyzed, forexample up to 10%. The proportion of grafted-on vinylformamide units ispreferably from 20 to 40% by weight, based on polyalkylene glycol.Polyethylene glycols having molar masses from 2000 to 10 000 arepreferably used.

Zwitterionic polyalkylene polyamines and zwitterionic polyethyleniminesare also suitable for stabilizing the oil-in-water emulsions. Suchcompounds are disclosed, for example, in EP-B-0 112 592. They areobtainable, for example, by first alkoxylating a polyalkylenepolyamineor polyethylenimine, for example with ethylene oxide, propylene oxideand/or butylene oxide and then quaternizing the alkoxylation products,for example with methyl bromide or dimethyl sulfate, and then sulfatingthe quaternized, alkoxylated products with chlorosulfonic acid or sulfurtrioxide. The molar mass of the zwitterionic polyalkylenepolyamine is,for example, from 1000 to 9000, preferably from 1500 to 7500. Thezwitterionic polyethylenimines preferably have molar masses in the rangeof from 1500 to 7500 Dalton. The other, abovementioned stabilizers areused, if appropriate, in combination with a surfactant for stabilizingthe emulsions. If they are employed, they are used, for example, inamounts of from 0.05 to 15% by weight, preferably from 0.5 to 5% byweight, based on the monomers.

In order to obtain stable aqueous polymer dispersions, polymerizationcan, if appropriate, additionally be carried out in the presence ofprotective colloids. They have as a rule average molar masses M_(w)above 500, preferably of more than 1000. Examples of protective colloidsare polyvinyl alcohols, cellulose derivatives, such ascarboxymethylcellulose, polyvinylpyrrolidone, polyethylene glycols,graft polymers of vinyl acetate and/or vinyl propionate on polyethyleneglycols, polyethylene glycols endcapped at one or both ends with alkyl,carboxyl or amino groups, polydiallyldimethylammonium chlorides and/orpolysaccharides, such as, in particular, water-soluble starches, starchderivatives and proteins. Such products are described, for example, inRompp, Chemie Lexikon 9th edition, volume 5, page 3569 or inHouben-Weyl, Methoden der organischen Chemie, 4th edition, volume 14/2,section IV, Umwandlung von Cellulose und Starke by E. Husemann and R.Werner, pages 862-915 and in Ullmanns Encyclopedia for IndustrialChemistry, 6th edition, volume 28, page 533 et seq., underPolysaccharides.

For example, all types of starch are suitable, e.g. both amylose andamylopectin, natural starches, hydrophobically or hydrophilicallymodified starches, anionic starches, cationically modified starches,degraded starches, it being possible for the starch degradation to beeffected, for example, oxidatively, thermally, hydrolytically orenzymatically and for both natural and modified starches to be used forthe starch degradation. Further suitable protective colloids aredextrins and crosslinked water-soluble starches, which arewater-swellable.

Preferably used as a protective colloid are natural, water-solublestarches which, for example, can be converted into a water-soluble formwith the aid of starch digestion and anionically modified starches, suchas oxidized potato starch. Particularly preferred are anionicallymodified starches, the molecular weight of which can be reduced. Themolecular weight reduction is preferably carried out enzymatically. Theaverage molar mass M_(w) of the degraded starches is, for example, from500 to 100 000, preferably from 1000 to 30 000. The degraded starcheshave, for example, an intrinsic viscosity [η] of from 0.04 to 0.5 dl/g.Such starches are described, for example, in EP-B-0 257 412 and inEP-B-0 276 770. If protective colloids are used in the polymerization,the amounts used are, for example, from 0.5 to 50, in particular from 5to 40% by weight, in general from 10 to 30% by weight, based on themonomers used in the polymerization.

In order to modify the properties of the polymers, the polymerizationcan, if appropriate, be carried out in the presence of at least onepolymerization regulator. Examples of polymerization regulators areorganic compounds which comprise sulfur in bound form, such as dodecylmercaptan, thiodiglycol, ethylthioethanol, di-n-butyl sulfide,di-n-octyl sulfide, diphenyl sulfide, diisopropyl disulfide,2-mercaptoethanol, 1,3-mercaptopropanol, 3-mercaptopropane-1,2-diol,1,4-mercaptobutanol, thioglycolic acid, 3-mercaptopropionic acid,mercaptosuccinic acid, thioacetic acid and thiourea, aldehydes, such asformaldehyde, acetaldehyde and propionaldehyde, organic acids, such asformic acid, sodium formate or ammonium formate, alcohols such as, inparticular, isopropanol, and phosphorus compounds, such as sodiumhypophosphite. If a regulator is used in the polymerization the amountused in each case is, for example, from 0.01 to 5, preferably from 0.1to 1,% by weight, based on the monomers used in the polymerization.

The oil-in-water emulsion is subjected to free radical polymerization.The polymerization is effected in general in the presence of at leastone free radical polymerization initiator. All compounds which arecapable of initiating a polymerization are suitable as thepolymerization initiator. These are substantially peroxides,hydroperoxides, azo compounds and redox catalysts. Examples ofinitiators are described in WO-A-99/40123, page 32, line 45 to page 34,line 9. The polymerization can also be initiated by the action ofhigh-energy radiation, such as UV or actinic or radioactive radiation,the procedure being effected, if appropriate, in the presence of atleast one sensitizer. Those initiators which dissolve in the oil phaseare preferably used. The polymerization of the monomers in theminiemulsion can also be effected electrochemically, with the aid ofmicrowave radiation and/or by the action of ultrasound. Thepolymerization temperature is, for example, from 0 to 120° C.; it iscarried out at temperatures above 100° C. and under elevated pressure inpressure-resistant apparatuses. In general, the suspensionpolymerization of the oil-in-water emulsion is carried out in thetemperature range of from 0 to 95° C.

The invention also relates to a process for the preparation of aqueousdispersions of polymers which have an average particle diameter of atleast 1 μm and which comprise a fluorescent dye, by free radicalsuspension polymerization of ethylenically unsaturated monomers in anoil-in-water emulsion whose disperse phase comprises at least onefluorescent dye dissolved in at least one ethylenically unsaturatedmonomer and has an average particle diameter of at least 1 μm, in thepresence of a surface-active compound, the suspension polymerizationbeing carried out in the presence of at least 0.5% by weight, based onthe monomers, of at least one hydrophobic, nonpolymerizable, organiccompound, of a hydrophobic polymer of at least one C₂- to C₆-olefin, ofa siloxane having a molar mass M_(w) of up to 5000 and/or polystyrenehaving a molar mass M_(w) of up to 10 000.

The suspension polymerization is carried out, for example, in thepresence of from 0.5 to 50% by weight, preferably in the presence offrom 1 to 20% by weight, based on the monomers, of a hydrophobic,nonpolymerizable, organic compound, of a hydrophobic polymer of at leastone C₂- to C₆-olefin, of a siloxane having a molar mass M_(w) of up to5000 and/or of a polystyrene having a molar mass M_(w) of up to 10 000.The suspension polymerization is preferably carried out in the presenceof from 0.5 to 50% by weight of hexadecane and/or white oil,particularly preferably in the presence of from 2 to 20% by weight ofhexadecane and/or white oil.

The residual monomer content of the dispersions according to theinvention which are thus prepared can be reduced by chemicaldeodorization as described, for example, by P. H. H. Araujo, C. Sayer,J. G. R. Poco, R. Giudici, in Polymer Engineering and Science, 2002(42), 1442-1468, or disclosed in EP 1 375 530 B1.

The solids content of the aqueous dispersions is, for example, from 10to 60% by weight, preferably from 20 to 45% by weight and in general inthe range of from 30 to 45% by weight.

The dispersed polymer particles comprise the hydrophobic substance andat least one fluorescent dye. They have an average particle size of, forexample, from 1 to 100 μm, preferably from 1.1 to 25 μm and in generalfrom 1.1 to 4 μm and comprise at least one fluorescent dye in an amountof, for example, from 0.001 to 10% by weight, in general from 0.01 to1.0% by weight. The particle sizes of the finely divided polymer whichare stated here are weight average particle sizes, as can be determinedby light scattering. Methods for this purpose are familiar to the personskilled in the art, for example from H. Wiese in D. Distler, WässrigePolymerdispersionen, Wiley-VCH 1999, section 4.2.1, page 40 et seq., andliterature cited there, and H. Auweter, D. Horn, J. Colloid Interf. Sci.105 (1985) 399, D. Lilge, D. Horn, Colloid Polym. Sci. 269 (1991) 704 orH. Wiese, D. Horn, J. Chem. Phys. 94 (1991) 6429.

The dispersed particles have a uniform particle size distribution. Theuniformity can be characterized, for example, by the so-calleduniformity

$\frac{\sum{X_{i}{{{d\left( {v,0.5} \right)} - d_{i}}}}}{{d\left( {v,0.5} \right)}{\sum X_{i}}},$

where d_(i) is the average diameter of the size class i, X_(i) is themeasured contribution of this size class to the size distribution,d(v,0.5) is the volume-averaged median, and the sum is calculated ineach case over all size classes i (Mastersizer Reference Manual, MalvernInstruments Ltd., Spring Lane South, Malvern, Worcs. WR14 1AT, U.K.).Since the uniformity thus defined sums deviations from the volumeaverage, low values mean a greater uniformity. The particles producedaccording to the invention have a uniformity below 1.0 in scatteredlight measurements with evaluation according to the Mie theory.

Drying of the aqueous dispersions gives polymer particles which have anaverage particle size diameter of at least 1 μm and which comprise atleast one fluorescent dye, in the form of a powder. Examples of dryingmethods are spray drying and freeze drying. The individual particles arepresent in the powders in general as aggregates of a plurality ofindividual particles. They can be subjected, for example, to dry or wetmilling. For example, the aggregates of individual particles can bemilled to give particles having an average particle size of from 1 to100 μm. However, individual particles having an individual particlediameter of from 10 to 1000 nm, in general from 200 to 1000 nm may alsoform during the milling process. These particle sizes are then in therange which is characteristic for polymer particles which are producedby miniemulsion polymerization, for example according to the processdisclosed in WO-A-99/40123.

The invention also relates to the use of aqueous dispersions ofpolymers, which are obtainable by free radical suspension polymerizationor by free radical miniemulsion polymerization of ethylenicallyunsaturated monomers in an oil-in-water emulsion whose disperse phasecomprises at least one fluorescent dye dissolved in at least oneethylenically unsaturated monomer and has an average particle diameterof at least 10 nm, in the presence of at least one surface-activecompound and at least 0.5% by weight, based on the monomers, of at leastone hydrophobic, nonpolymerizable, organic compound, of a hydrophobicpolymer of at least one C₂- to C₆-olefin having a molar mass M_(w) of upto 10 000, of a siloxane having a molar mass M_(w) of up to 5000 and/orpolystyrene having a molar mass M_(w) of up to 10 000.

and of the powders obtainable from these polymer dispersions in eachcase by drying and comprising at least one fluorescent dye for themarking of materials.

Preferably, the aqueous dispersions of polymers which comprise at leastone fluorescent dye and a hydrophobic substance and have an averageparticle size of the dispersed particles of from 1 μm to 100 μm, inparticular from 1.1 to 25 μm, which dispersions can be prepared bysuspension polymerization, are used for the marking of materials.However, the aqueous dispersions obtainable by miniemulsionpolymerization by the process disclosed in WO-A-99/40123 and having anaverage particle diameter of <500 nm, the suitable dispersionscomprising at least one fluorescent dye, and dispersions whose polymerparticles have an average particle diameter of from >500 nm to 1000 nmand comprise at least one fluorescent dye can also be used. Suchdispersions can be prepared, for example, by bringing the averageparticle size of the droplets emulsified in water and comprising asolution of at least one hydrophobic, ethylenically unsaturated monomer,at least one hydrophobic substance and at least one fluorescent dye to avalue in the range of from >500 nm to 1000 nm by emulsification, andsubjecting the oil-in-water emulsion thus obtainable to free radicalpolymerization in a known manner by the suspension polymerizationmethod.

The aqueous dispersions according to the invention and the aqueousdispersions of polymers which comprise in each case at least onefluorescent dye and one hydrophobic substance, which dispersions areobtainable by miniemulsion polymerization, and the polymer powders whichcan be prepared from the dispersions by, for example, spray drying areused, for example, for the marking of textiles, paper, paperproductions, finishes, starting materials for the building industry,adhesives, fuels, plastics films, paper coating slips, paper sizes,liquid formulations for crop protection, pharmaceutical and cosmeticformulations, printing inks for the printing of packagings, paper anddata media. Of particular practical importance is the use of the aqueousdispersions according to the invention and of the aqueous dispersions ofpolymers which comprise in each case at least one fluorescent dye and ahydrophobic substance, which dispersions are obtainable by miniemulsionpolymerization, and the polymer powders which can be prepared from thedispersions by, for example, spray drying for the marking of packagingsof all types. The application can be effected, for example, directly,e.g. by spraying a polymer dispersion or together with a printing ink.The packagings may be, for example, paper, board, cardboard, plasticsfilms, such as films of polyethylene, polypropylene, polyester orpolyamide, or composite materials, e.g. composites comprising paper andat least one plastics film, composites comprising a metal foil and atleast one plastics film, such as blister films for the packaging oftablets, or composites comprising at least two different plastics films.The plastics films can, if appropriate, be coated on one or both sideswith a dispersion, e.g. a polyvinylidene chloride dispersion. In thecase of these composites—as already mentioned above—either paper or apaper product or a plastics film is marked with a dispersion to be usedaccording to the invention or with the aqueous dispersions of polymerswhich comprise in each case at least one fluorescent dye and ahydrophobic substance, which dispersions are obtainable by miniemulsionpolymerization, or with the polymer powders obtainable in each case fromthe dispersions.

The aqueous dispersions comprising at least one fluorescent dye arepreferably used for the marking of paper, paper products, finishes,adhesives, paper coating slips, paper sizes and liquid formulations forcrop protection. They are added, for example, to the substances to bemarked, in an amount which in most cases is such that the marking isundetectable or virtually undetectable in or on the materials with thenaked eye. The marking is detected, for example, with the aid of laserscanning microscopy, with the aid of a fluorescence microscope or withthe aid of a fluorescence spectrometer. The solids content of theaqueous dispersions is usually from 1 to 70% by weight, preferably from10 to 50% by weight. These dispersions can be used directly or afterdilution with a dispersing medium, preferably water, for the marking ofmaterials.

In order to mark materials, the aqueous polymer dispersions comprisingat least one fluorescent dye or the powders obtained therefrom are usedin amounts such that the fluorescent dyes are detectable in the markedmaterials. For example, from 0.01 to 25% by weight, preferably from 0.1to 5% by weight, of at least one type of polymeric dispersion particleswhich comprise at least one fluorescent dye are used for the marking ofpaper, paper coating slips, sizes, adhesives, cement plasticizers,primers in the building sector and finishes. For example, the papercoating slips marked according to the invention are applied with the aidof a coating unit to base paper in an amount of, for example, 11 g/m²and the coated paper is dried.

In addition to the aqueous dispersions according to the invention, whichcomprise at least one fluorescent dye, the paper coating slips comprisethe constituents customary for paper coating slips, such as pigments,dispersants, thickeners and binders. The binders are usually emulsionpolymers which preferably comprise at least 40% by weight, preferably atleast 60% by weight, particularly preferably at least 80% by weight, ofso-called main monomers.

Preferred main monomers are C₁-C₁₀-alkyl (meth)acrylates and mixtures ofalkyl (meth)acrylates with vinylaromatics, in particular styrene (alsosummarized as polyacrylate binder compositions), or hydrocarbons having2 double bonds, in particular butadiene, or mixtures of suchhydrocarbons with vinylaromatics, in particular styrene (also summarizedas polybutadiene binder compositions).

In the case of polybutadiene binder compositions, the weight ratio ofbutadiene to vinylaromatics (in particular styrene) may be, for example,from 10:90 to 90:10, preferably from 20:80 to 80:20.

In addition to the main monomers, the polymer may comprise furthermonomers, e.g. monomers having carboxyl, sulfo or phosphonic acidgroups. Carboxyl groups are preferred. For example, acrylic acid,methacrylic acid, itaconic acid, maleic acid or fumaric acid andaconitic acid may be mentioned. The content of ethylenically unsaturatedacids in the emulsion polymer is in general less than 5% by weight.

Further monomers are, for example, also monomers comprising hydroxylgroups, in particular C₁-C₁₀-hydroxyalkyl (meth)acrylates, or amidessuch as (meth)acrylamide.

Such binders are available, for example, under the trade names Styronal®and Acronal® (both from BASF Aktiengesellschaft).

According to the invention, these binders are first mixed with theaqueous dispersions according to the invention which comprise at leastone fluorescent dye. The binder compositions thus obtained are then usedfor the preparation of a paper coating slip.

The present invention therefore also relates to binder compositionswhich comprise a binder and dispersions according to the inventioncomprising at least one fluorescent dye.

The present invention furthermore also relates to a paper coating slipwhich comprises such a binder composition.

Paper can also be marked by using, in papermaking, a paper size whichcomprises an aqueous polymer dispersion comprising at least onefluorescent dye. Suitable engine sizes for paper are, for example,aqueous polymer dispersions, aqueous emulsions of alkyldiketenes oralkenylsuccinic anhydrides or rosin size. Surface sizes for paper mayalso comprise an aqueous polymer dispersion comprising at least onefluorescent dye and can themselves be marked therewith and can also beused for the marking of paper and paper products.

The present invention therefore also relates to paper sizes whichcomprise aqueous dispersions according to the invention comprising atleast one fluorescent dye.

For marking of paper and paper products, it is of course also possibleto apply an aqueous polymer dispersion comprising at least onefluorescent dye or powders obtained therefrom directly to the surface ofpaper or paper products, such as board or cardboard. The application ofthe aqueous polymer dispersion comprising at least one fluorescent dyeto a paper product can be effected, for example, with the aid of a sizepress or with the aid of a spray apparatus. It is also possible to sprayor to print the aqueous dispersion required for the marking only onparts of a paper product in order to mark the product partially, forexample as a barcode. Such markings are of interest, in particular forpackaging materials. The polymer particles which comprise a fluorescentdye can be localized, for example, by means of confocal laser scanningmicroscopy and can be uniquely identified on the marked materials byfluorescence spectroscopy.

For the marking of fuels, in particular of heating oil, the aqueousdispersions of polymers which comprise at least one fluorescent dye, orthe powders obtainable therefrom by spray drying, are used, for example,in an amount of, for example, from 0.00001 to 1% by weight, preferablyfrom 0.0001 to 0.1% by weight, based on fuel, the data for thedispersions being based on the solids content of the dispersion. For themarking of liquid formulations for crop protection, pharmaceutical andcosmetic formulations, the polymer particles of the aqueous polymerdispersions comprising at least one fluorescent dye or the powdersobtainable therefrom by spray drying are used, for example, in amountsof from 0.00001 to 1% by weight, preferably from 0.0001 to 0.2% byweight, in general from 0.0001 to 0.1% by weight. The liquidformulations for crop protection are usually aqueous formulations, suchas emulsions or dispersions of, for example, pesticides, herbicides orfungicides.

The polymer particles which comprise at least one fluorescent dye andare used according to the invention for the marking of materials arelightfast. They are moreover stable to migration, i.e. they do notbleed.

EXAMPLES Example 1

The following mixture was initially taken in a 2 l kettle which wasequipped with a dispenser stirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol (Mowiol ® 40/88 (10% in water)52.5 mg of NaNO₂ 30 g of allyl methacrylate 270 g of methyl methacrylate0.06 g of yellow fluorescent dye - Yellow 083 (Lumogen ® F) 15 g ofhexadecane

The mixture was dispersed for 30 min at room temperature at a speed of5000 rpm and then transferred to a 2 l kettle equipped with an anchorstirrer. 1.575 g of tert-butyl perpivalate were added and the kettle washeated to 60° C. in the course of 1 hour. The kettle content was thenheated to 70° C. over 2 hours, then to 85° C. in 30 min and kept at thistemperature for 1 hour. 7 g of a 10% strength aqueous solution oftert-butyl hydroperoxide were added and a solution of 0.4 g of ascorbicacid and 20 g of water was metered in over one hour. The kettle was thencooled to room temperature.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a volume-averaged particle diameter of 2.0 μm and a narrowparticle size distribution with a uniformity of 0.5, determined by meansof light scattering analysis according to the Mie theory (MalvernMastersizer) was obtained, a refractive index of 1.49 and an absorptionindex of 0 being taken as the basis for the particles. The solidscontent was 30.85% by weight.

Example 2

The following mixture was initially taken in a 2 l kettle which wasequipped with a dispenser stirrer (diameter 5 cm):

441.45 g of water 45 g of polyvinyl alcohol (Mowiol ® 15/79 (10% inwater) 180 g of Culminal ® MHPC 100 (5% in water),methylhydroxypropylcellulose 52.5 mg of NaNO₂ 30 g of butanedioldiacrylate 270 g of methyl methacrylate 0.06 g of yellow fluorescentdye - Yellow 083 (Lumogen ® F) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1. A dispersion of crosslinkedparticles colored with fluorescent dye and having an average particlediameter of 2.6 μm and a narrow particle size distribution with auniformity of 0.5 was obtained. The solids content of the dispersion was29.6% by weight.

Example 3

The following mixture was initially taken in a 2 l kettle which wasequipped with a dispenser stirrer (diameter 5 cm):

450 g of water 250 g of Mowiol ® 40/88 (10% in water), partly hydrolyzedpolyvinyl alcohol 52.5 mg of NaNO₂ 15 g of allyl methacrylate 285 g ofmethyl methacrylate 0.1 g of yellow fluorescent dye - (Lumogen ® FYellow 083) 0.1 g of orange fluorescent dye (Lumogen ® F - Orange 240)0.1 g of red fluorescent dye (Lumogen ® F - Red 300) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1. A dispersion of crosslinkedparticles colored with 3 fluorescent dyes and having an average particlediameter of 1.8 μm and a narrow particle size distribution with auniformity of 0.4 was obtained. The solids content of the dispersion was31.5% by weight.

Example 4

The following mixture was initially taken in a 2 l kettle which wasequipped with a dispenser stirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 52.5 mg of NaNO₂ 30 g of allyl methacrylate 270 g of methylmethacrylate 0.06 g of yellow fluorescent dye (Lumogen ® F - Yellow 083)0.3 g of red fluorescent dye (Lumogen ® F - Red 300) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1. A dispersion of crosslinkedparticles colored with 2 fluorescent dyes and having a volume-averageparticle diameter of 1.8 μm and a narrow particle size distribution witha uniformity of 0.5 was obtained. The solids content of the dispersionwas 31% by weight.

Example 5

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 2.1 g of NaNO₂ (2.5% in water) 30 g of butanediol diacrylate 270g of methyl methacrylate 0.09 g of red fluorescent dye (Lumogen ® F -Red 305) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 2.4 μm and a uniformity of 0.5 wasobtained. 10 g of coagulum were found. After physical deodorization, thesolids content of the dispersion was 33.4% by weight.

Example 6

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 52.5 g of NaNO₂ (2.5% in water) 30 g of allyl methacrylate 270 gof methyl methacrylate 0.03 g of yellow fluorescent dye (Lumogen ® F -Yellow 083) 0.06 g of orange fluorescent dye (Lumogen ® F - Orange 240)0.09 g of red fluorescent dye (Lumogen ® F - Red) 15 g of hexadecane

The mixture was dispersed for 60 min at room temperature at a speed of6500 rpm and then transferred to a 2 l kettle equipped with an anchorstirrer. 1.575 g of tert-butyl perpivalate were added and the kettle washeated to 65° C. in the course of 1 hour. Thereafter, heating to 70° C.over 2 hours and then to 85° C. in 30 min was effected and thistemperature was maintained for 1 hour. 7 g of a 10% aqueous solution oftert-butyl hydroperoxide were added and a solution of 0.4 g of ascorbicacid in 20 g of water was metered in over one hour. The kettle was thencooled to room temperature.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 1.91 μm and a uniformity of 0.5 wasobtained. The solids content of the dispersion was 31.7% by weight.

Example 7

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

502.7 g of water 30 g of polyvinyl alcohol [Mowiol ® 15/79 (10% inwater)] 120 g of Culminal ® MHPC 100 (5% in water),methylhydroxypropylcellulose 52.5 mg of NaNO₂ 120 g of butanedioldiacrylate 150 g of methyl methacrylate 30 g of methacrylic acid 0.06 gof yellow fluorescent dye (Lumogen ® F - Yellow 083) 0.015 g ofhydroquinone monomethyl ether 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 4.9 μm was obtained. The solidscontent of the dispersion was 30.3% by weight.

Example 8

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 2.1 g of NaNO₂ (2.5% in water) 30 g of allyl methacrylate 240 gof methyl methacrylate 30 g of n-butyl acrylate 0.09 g of redfluorescent dye (Lumogen ® F - Red 305) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 2.1 μm and a uniformity of 0.4 wasobtained. 6 g of coagulum were found and the solids content of thedispersion was 29.9% by weight.

Example 9

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

370.1 g of water 208.3 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 1.75 g of NaNO₂ (2.5% in water) 25 g of butanediol diacrylate225 g of methyl methacrylate 0.75 g of ethylhexyl thioglycolate 0.08 gof red fluorescent dye (Lumogen ® F - Red 305) 12.5 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 1.6 μm and a uniformity of 0.4 wasobtained, and the solids content of the dispersion was 28.3% by weight.

Example 10

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 2.1 g of NaNO₂ (2.5% in water) 1.35 g of butanediol diacrylate298.65 g of methyl methacrylate 0.09 g of red fluorescent dye (Lumogen ®F - Red 305) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 1.9 μm and a uniformity of 0.5 wasobtained, and the solids content of the dispersion was 31.4% by weight.

Example 11

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 2.1 g of NaNO₂ (2.5% in water) 300 g of methyl methacrylate 0.09g of red fluorescent dye (Lumogen ® F - Red 305) 15 g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 1, the total amount of tert-butylperpivalate being divided into three equal parts. The first part wasadded at 60° C., the second part at 65° C. and the third part at 70° C.

A dispersion of uncrosslinked particles colored with a fluorescent dyeand having a mean particle diameter of 1.5 μm and a uniformity of 0.4was obtained, and the solids content of the dispersion was 31.3% byweight.

Example 12

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 2.1 mg of NaNO₂ 30 g of 1,4-butanediol diacrylate 270 g ofmethyl methacrylate 0.09 g of red fluorescent dye (Lumogen ® F - Red) 15g of white oil (CAS No. 8042-47-5)

The mixture was dispersed for 30 min at room temperature at a speed of5000 rpm and then transferred to a 2 l kettle equipped with an anchorstirrer. 2.1 g of tert-butyl perpivalate were added and the kettle washeated to 60° C. in the course of 1 hour. The kettle content was thenheated to 70° C. over 2 hours, then increased to 85° C. in 30 minutesand kept at this temperature for 1 hour. 7 g of a 10% strength aqueoussolution of tert-butyl hydroperoxide were added and a solution of 0.4 gof ascorbic acid in 20 g of water was metered in over one hour. Thekettle was then cooled to room temperature.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 1.2 μm and a broad particle sizedistribution was obtained. The solids content of the dispersion was27.6% by weight.

Example 13

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 40/88 (10% inwater)] 2.1 mg of NaNO₂ 24 g of 1,4-butanediol diacrylate 216 g ofmethyl methacrylate 0.09 g of red fluorescent dye (Lumogen ® F - Red) 60g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 12.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 1.2 μm and a broad particle sizedistribution was obtained. The solids content of the dispersion was29.0% by weight.

Example 14

The following mixture was added to a 2 l kettle having a dispenserstirrer (diameter 5 cm):

450 g of water 250 g of polyvinyl alcohol [Mowiol ® 26/88 (10% inwater)] 2.1 mg of NaNO₂ 30 g of 1,4-butanediol diacrylate 270 g ofmethyl methacrylate 0.09 g of red fluorescent dye (Lumogen ® F - Red) 15g of hexadecane

The emulsification of the mixture and the polymerization of the monomerswere effected as described in example 12.

A dispersion of crosslinked particles colored with a fluorescent dye andhaving a mean particle diameter of 1.2 μm and a narrow particle sizedistribution was obtained. The solids content of the dispersion was29.0% by weight.

Use Examples Formulation of Paper Coating Slips

The coating slips stated in the table below were prepared in a 1 lcontainer. pH was about 9 and the viscosity was adjusted to 1000 mPa·s.

TABLE Composition (1) (2) (3) (4) (5) (6) (7) CaCO₃ pigment 100.0 70.070.0 70.0 70.0 70.0 70.0 (Hydrocarb 90) Clay pigment 97.0 30.0 30.0 30.030.0 30.0 30.0 (Amazon 88) Dispersant 45.3 0.30 0.30 0.30 0.30 0.30 0.30(Polysalz S) NaOH 25.0 0.05 0.05 0.05 0.05 0.05 0.05 Styrene butadiene49.7 10.0 10.0 10.0 10.0 10.0 10.0 binder Styronal ® D 808 Thickener40.5 0.30 0.30 0.30 0.30 0.30 0.30 (Sterocoll ®) Marker 30.9 1.0 0.5 0.20.1 0.010 0.200 dispersion 1 Marker 32.5 1.0 0.5 0.2 0.1 0.010 0.400dispersion 2 Marker 31.1 1.0 0.5 0.2 0.1 0.010 0.800 dispersion 3

In the notation customary in the field, the first data column of thetable, under (1) indicates the solids content of the starting materialsused, and each of the following 6 columns (2) to (7) indicate therelative concentrations, based on 100 parts of pigment (in this caseHydrocarb 90+Amazon 88), for one use example in each case.

The dispersion prepared according to example 3 was used as markerdispersion 1.

Marker dispersion 2 was prepared analogously to the dispersion accordingto example 3 but comprised only the red fluorescent dye (Lumogen® F—Red300) with the same total dye concentration.

Marker dispersion 3 was likewise prepared analogously to example 3, butwith the dyes Lumogen® F—Red 300 and Lumogen® F—Yellow 083 in the sameproportions. The dispersion consisted of two-color particles.

The coating slip was then applied to a base paper from Scheufelen bymeans of a doctor blade so that a coat weight of 15 g/m² was obtained.The papers coated in this manner were then dried using a suitable dryingunit. The marking of the paper by the fluorescent marker particles isundetectable with the naked eye, but a spectroscopic examination bymeans of laser scanning microscopy permitted unambiguous identificationof all particle types used for the marking.

Marking of Paper Sizes

Marker particles produced according to the invention were used in thesurface finishing of paper. For this purpose, the marker dispersions 1,2 and 3 were mixed with Basoplast® 400DS, a standard dispersion ofacrylate copolymers, and this mixture was then stirred into an aqueousstarch solution (ratio of synthetic product to starch about 1:100). Theprepared mixture had a solids content of from 8 to 15% and was appliedin this form as a film to paper by means of a doctor blade. The coatweight was about 2 g/m² of starch, corresponding to 0.02 g/m² ofpolymer. In spectroscopic examinations by means of laser scanningmicroscopy, the marker particles used could be unambiguously identified.

Marking of Film Coatings

0.75 ml or 1.5 ml and 15 ml of a marker dispersion according to example3 or analogously prepared dispersions of one- and two-colored particleshaving the same total concentration of dye of the types Lumogen®) F—Red300 or Lumogen® F—Red 300 and Lumogen® F—Orange 240 were mixed into 1 kgof a 45% strength dispersion of the sealable acrylate Epotal® A 816 andthe mixture was applied by means of an airbrush to a BOPP film (MB 200from ExxonMobil) which was electrically pretreated and primed with a PUdispersion (Epotal® P 350) beforehand. In spectroscopic examinations bymeans of laser scanning microscopy, the marker particles used could beunambiguously identified.

1. An aqueous dispersion of polymers which have a particle diameter ofat least 1 μm and comprise a fluorescent dye, wherein said dispersion isobtainable by free radical suspension polymerization of ethylenicallyunsaturated monomers in an oil-in-water emulsion whose disperse phasecomprises at least one fluorescent dye dissolved in at least oneethylenically unsaturated monomer and has an average particle diameterof at least 1 μm, in the presence of at least one surface-activecompound and at least 0.5% by weight, based on the monomers, of at leastone hydrophobic, nonpolymerizable, organic compound, of a hydrophobicpolymer of at least one C₂ to C₆-olefin having a molar mass M_(w) of upto 10 000, of a siloxane having a molar mass M_(w) of up to 5000 and/orpolystyrene having a molar mass M_(w) of up to 10
 000. 2. The aqueousdispersion according to claim 1, wherein (a) hydrophobic monomers fromthe group consisting of C₁- to C₈-alkyl esters of acrylic acid, C₁- toC₈-alkyl esters of methacrylic acid, vinyl acetate, vinyl propionate,vinyl butyrate, styrene, chlorostyrene and/or α-methylstyrene, (b) ifappropriate, hydrophilic monomers from the group consisting ofethylenically unsaturated C₃- to C₆-carboxylic acids, vinylsulfonicacid, 2-acrylamido-2-methylpropanesulfonic acid, sulfopropyl acrylate,sulfopropyl methacrylate, styrenesulfonic acid, salts of said acids,acrylonitrile, methacrylonitrile, C₁- to C₈-hydroxyalkyl esters of C₁-to C₆-carboxylic acids, di-C₁- to C₃-alkylamino-C₂- to C₄-alkylacrylates, di-C₁- to C₃-alkylamino-C₂- to C₄-alkyl methacrylates,acrylamide, methacrylamide, N-vinylformamide and/or N-vinylpyrrolidoneand (c) if appropriate, at least one crosslinking monomer having atleast two double bonds in the molecule are used as ethylenicallyunsaturated monomers.
 3. The aqueous dispersion according to claim 1,wherein the monomer mixtures used in the polymerization comprise (a)from 60 to 100% by weight of at least one hydrophobic monomer, (b) from0 to 30% by weight of at least one hydrophilic monomer and (c) from 0 to40% by weight of at least one crosslinking monomer having at least twodouble bonds.
 4. The aqueous dispersion according to claim 1, whereinthe monomer mixtures used in the polymerization comprise (a) from 60 to99.9% by weight of at least one hydrophobic monomer, (b) from 0 to 30%by weight of at least one hydrophilic monomer and (c) from 0.1 to 25% byweight of at least one crosslinking monomer.
 5. The aqueous dispersionaccording to claim 1, wherein aliphatic or aromatic hydrocarbons having10 to 50 carbon atoms, alcohols having 10 to 24 carbon atoms,tetraalkylsilanes, olive oil, perfluoromethyldecalin and/or di-n-butylesters of C₄- to C₆-dicarboxylic acids are used as the hydrophobic,nonpolymerizable, organic compound.
 6. The aqueous dispersion accordingto claim 1, wherein homopolymers of at least one C₂- to C₆-olefin orcopolymers of C₂- to C₆-olefins having a molar mass M_(w) of up to 10000, siloxanes having a molar mass Mw of up to 5000 and/or polystyrenehaving a molar mass M_(w) of up to 10 000 are used as hydrophobicpolymers.
 7. The aqueous dispersion according to claim 1, whereinhexadecane and/or white oil in an amount of from 0.5 to 50% by weight,based on the monomers, is used as the hydrophobic, nonpolymerizablecompound.
 8. The aqueous dispersion according to claim 1, wherein thedispersed polymer particles have an average particle size of from 1.1 to25 μm and comprise at least one fluorescent dye in an amount of from0.001 to 10% by weight.
 9. A process for the preparation of aqueousdispersions of polymers which have an average particle diameter of atleast 1 μm and comprise a fluorescent dye by free radical suspensionpolymerization of ethylenically unsaturated monomers in an oil-in-wateremulsion whose disperse phase comprises at least one fluorescent dyedissolved in at least one ethylenically unsaturated monomer and has anaverage particle diameter of at least 1 μm, in the presence of at leastone surface-active compound, wherein the suspension polymerization iscarried out in the presence of at least 0.5% by weight, based on themonomers, of at least one hydrophobic, nonpolymerizable organiccompound, of a hydrophobic polymer of at least one C₂- to C₆-olefin, ofa siloxane having a molar mass M_(w) of up to 5000 and/or polystyrenehaving a molar mass M_(w) of up to 10
 000. 10. The process according toclaim 9, wherein the suspension polymerization is carried out in thepresence of from 0.5 to 50% by weight, based on the monomers, of ahydrophobic, nonpolymerizable, organic compound, of a hydrophobicpolymer of at least one C₂- to C₆-olefin, siloxanes having a molar massM_(w) of up to 5000 and/or polystyrene having a molar mass M_(w) of upto 10
 000. 11. The process according to claim 9, wherein the suspensionpolymerization is carried out in the presence of from 1 to 20% byweight, based on the monomers, of a hydrophobic, nonpolymerizable,organic compound, of a hydrophobic polymer of at least one C₂- toC₆-olefin, of a siloxane having a molar mass M_(w) of up to 5000 and/ora polystyrene having a molar mass M_(w) of up to 10
 000. 12. The processaccording to any claim 9, wherein the suspension polymerization iscarried out in the presence of from 2 to 10% by weight of hexadecaneand/or white oil.
 13. A polymer particle which has an average particlediameter of at least 1 μm and comprises at least one fluorescent dye,wherein said polymer particle is obtainable by drying the aqueousdispersions according to claims
 1. 14. The method of obtaining anaqueous dispersions of polymers by free radical suspensionpolymerization or by free radical miniemulsion polymerization ofethylenically unsaturated monomers in an oil-in-water emulsion whosedisperse phase comprises at least one fluorescent dye dissolved in atleast one ethylenically unsaturated monomer and has an average particlediameter of at least 100 nm, in the presence of at least onesurface-active compound and at least 0.5% by weight, based on themonomers, of at least one hydrophobic, nonpolymerizable, organiccompound, of a hydrophobic polymer of at least one C₂- to C₆-olefinhaving a molar mass M_(w) of up to 10 000, of a siloxane having a molarmass M_(w) of up to 5000 and/or polystyrene having a molar mass M_(w) ofup to 10 000, and of the powder obtainable from these polymerdispersions in each case by drying and comprising at least onefluorescent dye for the marking of materials.
 15. The method accordingto claim 14, wherein the aqueous dispersions of polymers which compriseat least one fluorescent dye and a hydrophobic substance and have anaverage particle diameter of the dispersed particles of from 1 μm to 100μm, in particular from 1.1 to 25 μm, which dispersions can be preparedby suspension polymerization, are used for the marking of materials. 16.The method according to claim 14, wherein the aqueous dispersions or thepolymer particles comprising at least one fluorescent dye are used forthe marking of textiles, paper, paper products, finishes, startingmaterials for the building industry, adhesives, fuels, plastics films,paper coating slips, paper sizes, liquid formulations for cropprotection, pharmaceutical and cosmetic formulations, printing inks forthe printing of packagings, paper and data media.
 17. A bindercomposition comprising a binder and an aqueous dispersion according toclaim
 1. 18. A paper coating slip comprising a binder compositionaccording to claim
 17. 19. A paper size comprising an aqueous dispersionaccording to claim 1.